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We explored the use of pulsed flow modulation (PFM) two-dimensional comprehensive gas chromatography (GCxGC) mass spectrometry with supersonic molecular beams (SMB) (also named Cold electron ionization (EI)) for achieving universal pesticide analysis in agricultural products. The use of GCxGC serves as an alternative to MS-MS in the needed reduction of matrix interference while enabling full-scan MS operation for universal pesticide analysis with reduced number of false negatives. Matrix interference is further reduced with Cold EI in view of the enhancement of the molecular ions. Pulsed flow modulation is a simple GCxGC modulator that does not consume cryogenic gases while providing tuneable second GCxGC column injection time for enabling the use of quadrupole-based mass spectrometry regardless its limited scanning speed. PFM-GCxGC-MS with Cold EI combines improved separation of GCxGC with Cold EI benefits of tailing-free ultra-fast ion source response time and enhanced molecular ions for the provision of increased sample identification information and reduced matrix interference. Consequently, PFM GCxGC-MS with Cold EI also improved NIST library identification probabilities of the spiked pesticides. PFM GCxGC is further characterized by largely increased second column sample and matrix capacity that as a result performs much better than thermal modulation GCxGC-MS with standard EI in the suppression of matrix interference. In a comparison with standard GC-MS, we measured with PFM GCxGC-MS with Cold EI an average total ion count matrix interference reduction factor of 32 for 12 pesticides in two matrices of baby leaves mixture and lettuce. In addition, Cold EI further increases the range of pesticides amenable for GC-MS analysis and its response is relatively uniform hence with it the need for pesticides specific calibration is reduced.Pulsed flow modulation GCxGC-MS with Cold EI significantly reduces matrix interference and improves sample identification. [ABSTRACT FROM AUTHOR]

An Open Probe inlet was combined with a low thermal mass (LTM) ultra fast gas chromatograph (GC) and mass spectrometer (MS) of GC–MS for obtaining real time analysis with separation. The Open Probe is based on a vaporization oven that is open to room air while having helium purge flow protection to eliminate air leakage into the oven and MS ion source. Sample introduction into the Open Probe is as simple as touch the sample, push the sample holder into the Open Probe oven and have the results in 20–30 s. The Open Probe is mounted onto the LTM fast GC that is coupled with the MS of either GC–MS with Cold EI or standard GC–MS. Open Probe fast GC–MS provides real time analysis in combination with GC separation, library identification, absence of ion suppression effects and uniform electron ionization response for improved quantitation, and it uses the low cost MS of GC–MS. The operation of the Open Probe fast GC–MS is demonstrated in the 20 s separation and 40 s full analysis cycle time of heroin in its street drug powder, cockroach repeller liquid residue on tomato in 30 s and trace TNT on human hand in 40 s. [ABSTRACT FROM AUTHOR]

Abstract: Several novel synthetic organic compounds were successfully analyzed with a unique type of GC–MS titled Supersonic GC–MS following a failure in their analysis with standard GC–MS. Supersonic GC–MS is based on interfacing GC and MS with a supersonic molecular beam (SMB) and on electron ionization of sample compounds as vibrationally cold molecules while in the SMB, or by cluster chemical ionization. The analyses of novel synthetic organic compounds significantly benefited from the extended range of compounds amenable to analyses with the Supersonic GC–MS. The Supersonic GC–MS enabled the analysis of thermally labile compounds that usually degrade in the GC injector, column and/or ion source. Due to the high carrier gas flow rate at the injector liner and column these compounds eluted without degradation at significantly lower elution temperatures and the use of fly-through EI ion source eliminated any sample degradation at the ion source. The cold EI feature of providing trustworthy enhanced molecular ion (M+), complemented by its optional further confirmation with cluster CI was highly valued by the synthetic organic chemists that were served by the Supersonic GC–MS. Furthermore, the provision of extended mass spectral structural, isomer and isotope information combined with short (a few minutes) GC–MS analysis times also proved beneficial for the analysis of unknown synthetic organic compounds. As a result, the synthetic organic chemists were provided with both qualitative and quantitative data on the composition of their synthetic mixture, and could better follow the path of their synthetic chemistry. Ten cases of such analyses are demonstrated in figures and discussed. [Copyright &y& Elsevier]

Describes a pulsed flame photometer detector (PFPD) design for gas chromatography with improved performance. Demonstration of detection limits; Reduction of the minimum detected amount of sulfur; Analysis of the factors affecting selectivity; Effect of the pulsed nature of the PFPD; Discussion of the difference between light guide and lens optics; Practical utilization of the PFPD.

Open Probe is based on a vaporization oven mounted on a transfer line of a gas chromatograph mass spedrometer (GC/MS) which is connected to the MS ion source via a short flow resthction capillary. The probe oven is open to room air while having helium purge flow protection to eliminate or significantly reduce air leakage into the oven and MS ion source. Sample analysis can be as simple as touch (the sample), push (the sample holder) into the open probe oven, and have the results. Experiments were performed with a GC/MS with supersonic molecular beams and with a standard Agilent 5975 MSD. Powders and tablets analysis were performed by touching the sample with the bottom side of a melting point vial and inserting it into the open probe oven with total analysis cycle lime of <30 s. Similarly, trace trinitrotoluene (TNT) on human fingerprints was analyzed. Additional sample holder types included swabs, spoons, and vials. The open probe is a leak-proof MS probe which is characterized by fast analysis cycle time, and it uses a low cost mass spectrometer of GC/MS with the benefits of electron ionization of library search and uniform, quantitative response without ion suppression effects. [ABSTRACT FROM AUTHOR]

Abstract: A quantitative answer cannot exist in analysis without a qualitative component to give enough confidence that the result meets the analytical needs (i.e. the result relates to the analyte and not something else). Just as a quantitative method must typically undergo an empirical validation process to demonstrate that it is fit for purpose, qualitative methods should also empirically demonstrate that they are suitable to meet the analytical needs. However, thorough qualitative method validation requires analysis of a great number of samples (possibly more than can be reasonably done), which is generally avoided due to the time and the effort involved. Instead, mass spectrometry (MS) is generally assumed to be the gold standard for qualitative methods, and its results are typically unquestioned. For example, a system was developed by European regulators of veterinary drug residues in food animals (2002/657/EC), in which the number of identification points given in MS analyses depends on the general degree of selectivity of the MS technique used. This well-defined approach gives a definite answer for decision-makers, so it has grown in popularity. However, the identification-points system is not scientific. The reality is that each situation requires information gathering and careful deductive thinking on the part of the analyst to make MS identifications. Rather than devise arbitrary requirements that need to be met by an unthinking analyst, we remind the analytical community that confirmation can be given only if two or more independent analyses are in agreement, preferably using orthogonally selective (independent) chemical mechanisms. In this article, we discuss the proper use of terminology, highlight the identification power of various MS techniques, demonstrate how MS identifications can fail if precautions are not taken, and re-assert the value of basic confirmation practices, qualitative method validation, information checklists, routine quality-control procedures, and blind proficiency-test analyses. [Copyright &y& Elsevier]

Abstract: Pulsed flow modulation (PFM) is based on higher flow rate time compression of the first GC column effluent, which prior to the injection into the second column is stored for a few seconds in a standard fused silica wide bore transfer line. We constructed the PFM device with two standard 1/16in. brass compression fittings with the insertion of the two columns inside the wide bore 0.53mm i.d. fused silica storage transfer line for the elimination of dead volumes. This simple arrangement provides a combination of flexibility in the length of the sample storage transfer line hence comprehensive two-dimensional gas chromatography (GC×GC) cycle time, inert sample path and full elimination of cooling gas consumption. A record short second column injection time of 20ms is demonstrated. Practical injection times are the sample collection time (such as 4s) divided by the second to first column flow rate ratio (such as 20/0.7), which is typically around 150ms. Due to the low cost of the device it can also be considered for use with non comprehensive time segmented GC×GC to remove a few accidental coelutions. PFM-GC×GC excels with high second column capacity due to the use of 0.32mm i.d. columns with high flow rates as the second dimension GC×GC column. As a result, PFM-GC×GC can have up to two orders of magnitude higher second column sample capacity and linear dynamic range for improved reduction of adverse matrix interference effects due to column overloading. [Copyright &y& Elsevier]

Gas chromatography–mass spectrometry (GC–MS) suffers from a major limitation in that an expanding number of thermally labile or low volatility compounds of interest are not amenable for analysis. We found that the elution temperatures of compounds from GC can be significantly lowered by reducing the column length, increasing the carrier gas flow rate, reducing the capillary column film thickness and lowering the temperature programming rate. Pyrene is eluted at 287 °C in standard GC–MS with a 30 m×0.25 mm I.D. column with 1-μm DB5ms film and 1-ml/min He column flow rate. In contrast, pyrene is eluted at 79 °C in our “Supersonic GC–MS” system using a 1 m×0.25 mm I.D. column with 0.1-μm DB5ms film and 100-ml/min He column flow rate. A simple model has been invoked to explain the significantly (up to 208 °C) lower elution temperatures observed. According to this model, every halving of the temperature programming rate, or number of separation plates (either through increased flow rate or due to reduced column length), results in ∼20 °C lower elution temperature. These considerably lower elution temperatures enable the analysis of an extended range of thermally labile and low volatility compounds, that otherwise could not be analyzed by standard GC–MS. We demonstrate the analysis of large polycyclic aromatic hydrocarbons (PAHs) such as decacyclene with ten fused rings, well above the current GC limit of PAHs with six rings. Even a metalloporphirin such as magnesiumoctaethylporphin was easily analyzed with elution temperatures below 300 °C. Furthermore, a range of thermally labile compounds were analyzed including carbamates such as methomyl, aldicarb, aldicarbsulfone and oxamyl, explosives such as pentaerythritol tetranitrate, Tetryl and HMX, and drugs such as reserpine (608 a.m.u.). Supersonic GC–MS was used, based on the coupling of a supersonic molecular beam (SMB) inlet and ion sources with a bench-top Agilent 6890 GC plus 5972 MSD. The Supersonic GC–MS provides enhanced molecular ion without any ion source related peak tailing. Thus, the lower GC separation power involved in the analysis of thermally labile and low volatility compounds is compensated by increased separation power of the MS gained from the enhanced molecular ion. Several implications of these findings are discussed, including our conclusion that slower chromatography leads to better analysis of thermally labile compounds. [Copyright &y& Elsevier]

• We report the novel and useful LTM-LPGC-MS technique for the first time. • A new working instrument for real-world application was developed. • LTM-LPGC-MS concepts, features, and trade-offs are described and evaluated. • Example applications with <1 min analysis cycle times are demonstrated. • Comparison of LTM-LPGC-MS is made with conventional fast GC-MS. Conventional gas chromatography - mass spectrometry (GC-MS) takes 20–40 min per sample, which is undesirably slow in any application if speed can be increased while still meeting analytical needs. In this study, we achieved reasonably good separations with full analysis cycle times of less than 1 min by combining for the first time low-pressure (LP) GC-MS with low thermal mass (LTM) resistive-heating for rapid temperature ramping and cooling of the capillary column. The analytical column is threaded into the LTM thin-walled metal tubing in an instrumental device known as "LTM Fast GC" that is mounted at the top of the gas chromatograph in a detector port. The column inlet and outlet are connected to the GC injector and MS transfer line as usual. For LPGC-MS, a 40 cm, 0.1 mm. i.d. uncoated flow restrictor capillary connected at the injector is coupled with a 2.6 m, 0.25 mm i.d., 0.25 µm film thickness analytical column leading to the MS. Thus, the inlet operates at normal GC pressures, but the analytical column is under vacuum, which increases the optimal helium carrier gas flow velocity thereby increasing speed of full range separations while maintaining acceptable quality of chromatography. This column configuration in LTM-LPGC-MS trades a 64-fold gain in speed of analysis vs. standard GC-MS for a 4-fold loss in chromatographic peak capacity, thereby converting analysis time from minutes into seconds in common applications. For example, jet fuel containing fatty acid methyl esters (akin to biofuel) was separated in 25 s with <1 min full analysis cycle time. An EPA Method 8270 mixture of 76 analytes was also analyzed in <1 min full cycle time by LTM-LPGC-MS. Other examples include very fast analysis of heroin in a street drug powder and elucidation of a new organic synthetic compound. In this report, we describe and discuss the several advantageous and practical features of LTM-LPGC-MS, as well as its trade-offs. [ABSTRACT FROM AUTHOR]

Abstract: A new approach of flow modulation comprehensive two-dimensional gas chromatography–mass spectrometry (GC×GC–MS) with supersonic molecular beam (SMB) and a quadrupole mass analyzer is presented. Flow modulation uniquely enables GC×GC–MS to be achieved even with the limited scan speed of quadrupole MS, and its 20ml/min column flow rate is handled, splitless, by the SMB interface. Flow modulation GC×GC–SMB–MS shares all the major benefits of GC×GC and combines them with GC–MS including: (a) increased GC separation capability; (b) improved sensitivity via narrower GC peaks; (c) improved sensitivity through reduced matrix interference and chemical noise; (d) polarity and functional group sample information via the order of elution from the second polar column. In addition, GC×GC–SMB–MS is uniquely characterized by the features of GC–MS with SMB of enhanced and trustworthy molecular ion plus isotope abundance analysis (IAA) for improved sample identification and fast fly-through ion source response time. The combination of flow modulation GC×GC with GC–MS with SMB (supersonic GC–MS) was explored with complex matrices such as diesel fuel analysis and pesticide analysis in agricultural products. [Copyright &y& Elsevier]

Abstract: We have combined the benefits of supersonic molecular beam interface and its related fly-through electron ionization (EI) ion source with the advanced features of the Varian 1200L gas chromatography–mass spectrometry (GC–MS) and mass spectrometry–mass spectrometry (MS–MS), resulting in a new and powerful GC–MS platform with record setting performance. Electron ionization of vibrationally cold molecules in the supersonic molecular beams (SMB) (cold EI) provided mass spectra with enhanced molecular ion, yet with good library search results and superior identification probabilities. We found that high GC column flow rates lower the elution temperature for any given compounds. This allows much larger molecules to elute at the maximum temperature of standard columns. We analyzed a mixture of heavy linear chain hydrocarbons all the way to C84H170 with a molecular weight of 1179.3amu, using a 4m 0.25mm i.d. column and 32ml/min He flow rate. Furthermore, we obtained a dominant molecular ion to all these compounds. The lower elution temperatures also greatly enhance the ability to analyze very thermally labile compounds such as carbamate pesticides. The experimental 1200 system is capable of triple quadrupole based MS–MS. We found that MS–MS on the molecular ion is much more effective than on fragment ions, and thus, the enhancement of the molecular ion directly improves the MS–MS sensitivity. Fast GC–MS analysis was also explored, based on very high column flow rate for fast splitless injections without affecting the sensitivity, and on the high system selectivity due to the combination of enhanced molecular ion and MS–MS. We demonstrate a few seconds long GC–MS–MS analysis of diazinon, spiked at 10ng/g in a mixed fruit and vegetable extract. The feature of enhanced molecular ion provides significant enhancement in the detection sensitivity via SIM and RSIM on the molecular ion. While octafluoronaphthalene (OFN) detection limit of below 1fg in SIM mode is shown, the harder is the compound analysis by standard GC–MS the greater is the gain in sensitivity by 1200-SMB. For example, the use of the 1200-SMB resulted in an improvement of over 50 times in the RSIM detection limit of cholesterol on its molecular ion at m/z =386, and decabromobiphenylether could be analyzed in SIM mode at 1ppb with S/N>50 (peak-to-peak noise). [Copyright &y& Elsevier]